Does anyone know if the standard Tibetan text of the Diamond Sutra was translated directly from Sanskrit, or from one of the Chinese translations, or something else? And does anyone know who first translated the Diamond into Tibetan? I've been looking and looking and can't find that information anywhere.

According to Michael Roach’s english translation (don’t know in light of recent events how authoratively we can take that but…)
“The translation of this sutra from Sanskrit into Tibetan, and its update into the newer translation standard, were completed by the Indian master Shilendra Bodhi and Yeshe De.”
Yeshe De (b.750?) was a disciple of Padmasambhava.
See: http://bookofchina300.blogspot.co.uk/2011/12/vajracchedika-prajnaparamita-sutra.html
Thanks Michael. I found another source that corroborates what Michael Roach wrote, so that’s what I’m going with.